1. Field of the Invention
The present invention is generally related to a zwitterionic-bias material, and more particularly to a zwitterionic-bias material for blood cell selection.
2. Description of the Prior Art
In general, leukocytes can be removed from blood, for example, by a fibrous type filter and besides the surface of such a leukocyte-removal filter medium is surface-treated to become positively charged because leukocytes and platelets are negatively charged. Thus, in addition to the sponge (porous) structure of the filter medium, the positively charged surface of the filter medium is also utilized to attract leukocytes and platelets. Besides, in order to avoid blood coagulation or platelet activation, usually a blood sample should be added with an anti-coagulant agent or the surface of the filter medium should be further surface-treated for anti-coagulation.
According to U.S. Pat. No. 5,407,581, a filter medium with a negatively charged surface for blood treatment is disclosed where fibrous PET (polyethylene terephthalate) is used as a substrate and a charged polymer is grafted on the surface of the substrate to have the fibrous PET (filter medium) be slightly negatively charged because a positively charged surface will cause the concentration increase of bradkinin to thereby result in inducing allergy during blood transfusion.
However, an eligible blood selection material should have selectivity among different types of blood cells but no blood coagulation or allergic response. In the prior report (U.S. Pat. No. 5,407,581), positively and negatively charged compounds can be used to obtain a surface showing positively charged, negatively charged, or neutral to have three types of charge representation but there are not only three types of blood responses to a material (or filter medium). Furthermore, for a neutral material (or filter medium), there is no charge at all or charge balance. That is, microscopic characteristics of a material (or filter medium), such as charge distribution in the case of charge balance, affect the blood response to a material. Therefore, developing a material having good blood cell selectivity is still an important subject.